1. Field of the Invention
This invention relates generally to radiating antennas and more specifically to antennas used to radiate microwave energy in microwave ovens.
2. Prior Art
U.S. Letters Pat. No. 3,320,396 issued to Helmut Boehm and assigned to Bowmar/TIC discloses an invention relating to ovens which is capable of employing microwave energy, together with conventional low frequency heat energy, for cooking food. One feature of that invention is the single broil element which serves both as an antenna for radiating microwave energy in the oven chamber and also as a resistor type heater. A major problem with the invention is the pattern of radiation of microwave energy. In essence the broil element functions similar to a straight line antenna. The radiation pattern in straight line antennas is shown best in FIG. 1. The main beam of radiation is tilted an angle .tau. (the phase angle) from the vertical, as shown in FIG. 1. Since the broil element or antenna, is disposed either at the top or bottom of the oven cavity, substantial amounts of power are radiated towards the upper or lower portion of the oven door causing hot spots to form and/or high currents to flow across the oven door or door gasket.
This radiation pattern becomes critical in microwave oven production since the oven door must be effectively sealed to prevent leakage of microwave energy from the oven chamber. The most common method to prevent this leakage is to employ a door seal or gasket. In the prior art devices hot spots or high current flow existed at or near the door seal and damaged or rendered it unusable within a short period of time.
The present invention solves this problem by altering the pattern of radiation by modifying the angle of radiation such that the main beam of radiation is not directed toward the door or door seal. Another benefit of the present invention is that it creates a more uniform distribution of microwave energy within the oven cavity thereby increasing the efficiency of the cooking unit.